Removal of highly unsaturated hydrocarbon impurities from diolefin-containing mixtures



' of synthetic rubber.

Patented Apr. 9, 1946 UNITED STATES PATENT OFFICE REMOVAL OF HIGHLYUNSATURATED HY- DROCARBON IMPURITIES FROM DIOLE- FIN -CONTA1N1NGMIXTURES Ludo K. Frevel, Midland, Mich., assignor to The Dow ChemicalCompan poration of Michigan y, Midland, Mich, a cor- No Drawing.Application July 26, 1943, Serial No. 496,184

14 Claims. ((71.260-(1815) conjugated diolefin, a minor amount of one ormore other unsaturated aliphatic hydrocarbons of equal or greater degreeof maturation may be treated to remove the latter without excessive lossor destruction of the diolefin, For convenience, such impurities arereferred to hereinas "highly unsaturated hydrocarbon impurities." Thehighly unsaturated hydrocarbon impurities accompanying a conjugateddiolefin are in most Serial No. 467,782, filed December 3, 1942-, and

adds to the teachings of the latter.

Conjugated diolefinsare produced in dilute form, but in largequantities, in various processes for the pyrolysis of petroleumfractions and other hydrocarbon starting materials. Thediolefincontaining mixtures obtained in such processes usuall comprise avariety of hydrocarbons other than the diolefins and separation of thelatter in a form suitable for use in the preparationof synthetic rubberhas proven diflicult. For instance, cracked-oil gas, which is awell-known source of diolefins, usually comprises paraflinic hydrocar:bons ranging from methane to hexane; olefins such as ethylene,propylene, butylenes,'amylenes,

and hexenes; diolefins such as allene, butadiene- 1.3, methyl-allene,isoprene, and piperylene; and

a small but appreciable amount of acetylenic hydrocarbons such asacetylene, methyl-acetylene, ethyl-acetylene and vinyl-acetylene; etc.

Although such mixture may be distilled to obtain fractions consistingfor the most part of hydrocarbons having the same number of carbon atomsin the molecule and the diolefin content of each fraction may beconcentrated by usual ual metals, copper and iron, but also alloys richpurification procedures, e. g. by extraction with solvents, theacetylenic hydrocarbons and other highly unsaturated hydrocarbonimpurities of close to the same boiling point as the diolefln tend toaccompany the latter during such treatments. For instance,butadiene-l'.3 which has been recovered from cracked-oil gas by suchconventional treatments usually retains a minor amount, e. g. less than0.1 molecular equivalent, of a'cetylenic hydrocarbons such asmethyl-acetylene, ethylacetylene and vinyl-acetylene, and may alsoretain asmall but appreciable proportion of un conjugated dioleflns suchas allene or methylallene. Such impurities are objectionable when thediolefin is to be employed in the production Although certaintreatments, e. g. with chemical agents, are known whereby the acetylenichydrocarbons maybe removed, such treatments are expensive or dimcult tocarry out and are not well suited to commercial practice.

It is an object of this invention to provide a simple inexpensive methodwhereby vapor mixturescomprising a conjugated diolefin and, asimpurities incident to the manufacture of the instancesalpha.beta-unsaturated aliphatic hydrocarbons having no hydrogen atomson the beta carbon atom, e. g. they are alpha-acetylenes or1.2-dioleflns. Other objects will be apparent from the followingdescription of the invention.

I have found that the transition elements, iron and copper, when infinely divided or porous condition, and also the oxides of these'metalshave the property of causing a selective destruction of such highlyunsaturated hydrocarbon impurities at temperatures below those at whichconjugated diolefins are rapidlydecomposed in the presence of theseinorganic substances and that by passing a vaporized conjugateddiolefin, containing such impurities, over the ironor copper-containingsubstance -at a suitable temperature, the highly unsaturated hydrocarbonimpurities may be destroyed without excessive loss or destruction of theconjugated diolefln. Other more saturated hydrocarbons, such as simpleoleflns and paraflinic hydrocarbons, if present in the vapor mixtureunder treatment, are substantially unaffected. I

It will be understood that not only the individin these metals may beused to effect the selective decomposition of the above-mentioned highlyunsaturated hydrocarbon impurities. similarly, the oxides ofthese metalsneed not be pure. Examh ples of such metal oxides are cuprous oxide, cu-

pric oxide, ferrousoxide, ferric oxide, ferrosoferric oxide, mixtures'ofsuch oxides, and the spinel, CuFe2O4. Although both the finely dividedmetals and their-oxides are eflfective for the purpose, the metaloxides, particularly the oxides of copper, are best adapted forcommercial use and are preferred. 1

The copper or iron, when used, is employed in a a, finely divided, ordispersed, or a finely porous form having a large surface relative toits absolute volume. The oxides of these metals often possess a finelyporous structure, and they may be employed in either powdered ordispersed form, or in the form of porous lumps, granules, or filaments,etc. If desired, the metal or metal oxide maybe deposited 'onlacan'iersuch as kaolin,

pumice, or alumina, etc., 'andbe used as a dis persionon, or in, suchcarrier material. The

carrier material should, of course, be one which is not itself acatalyst for the decomposition of conjugated diolefins at the operatingtemperav ture, and carrier materials which are nothighly of an oxide ofcopper or iron, and it is probable that these metal oxides also functionas catalysts, but in this instance, the metal oxide is often reducedeither to a lower oxide or to the metal, apparently by reaction with thehydrogen to form water.

The several metal oxides which may be employed differ as to the extentby which they are readily reduced during use in the process. Bothcuprous oxide and cupric oxide tend to be reduced ultimately to a finelyporous form of metallic copper. Ferric oxide is readily reduced toferro-soferric oxide, FeaOr, and it may be that the reduction sometimescontinues to form some ferrous oxide or even metallic iron. However, thelower oxides of iron, 1. e. F8304 and FeO, although effective ascatalystsfor the selective thermal decomposition of the highlyunsaturated hydrocarbon impurities, do not appear to have an appreciableoxidizing action toward such impurities under the reaction "conditionsemployed The observable function of ferric oxide and of the oxides ofcopper is that of serving as agents for the selective oxidation of thehighly unsaturated hydrocarbon impurities to form carbon and water vaporand leave the conjugated dioleflns largely unreacted.

Carbon produced in the reaction tends to accumulate in the catalyst bed,i. e. in the bed comprising the metal or metal oxide. It is a looseflufiy form of soot which does not interfere seriously with continuanceof the reaction for the selective oxidation of the highly unsaturatedhydrocarbon impurities. by means of a metal oxide, but which may, andoften does, interfere with the reaction for the selective thermaldecompo sition of said impurities unless the decomposition isaccompanied by oxidation. It appears that the water vapor formed by theselective oxidation reaction at leastmomentarily frees adjacent-metaloxide, or metal, surfaces of carbon and renders them available forcontinued reaction and that in the absence of such nascent water vaporthe catalyst surfaces tend to become coated with carbon and renderedunavailable to the decomposition reaction. However, the invention is notlimited.by this theory as to the reason for the results which areobserved.

In any instance, the catalyst becomes inactive after operating for sometime, due presumably to its becoming coated with carbon or tar. Whenusing ferric oxide or an oxide of copper in the process, the point atwhich the reaction for the destruction of the highly unsaturatedhydrocarbon impurities ceases, or becomes sluggish, corwhen thedecomposition is carried out in the presenceresponds roughly to that atwhich the metal oxide I has become reduced as described above. Thecarbonis then removed and the metal, or lower metal oxide, isre-oxidized by heating, e. g. to 350 C. or higher, in a current of airor other oxygencontaining gas. The resultant metal oxide, e. g. CuO orFezOa, is in condition for re-employment in the process.

It is because of the fact that ferric oxide and the oxides of copper arenot rendered inactive by the carbon formed in the process and thefurther fact that such oxide is formed during the step of freeing thecatalyst of carbon by oxidation, that these oxides are preferred overporous copper or porous iron as agents for effecting the selectivedecomposition of the highly unsaturated hydrocarbon impurities whichoften accompany conjugated dioleflns.

In practicing the invention, a vapor mixture comprising a conjugateddiolefin and a lesser amount, usually less than 0.1 molecularequivalent, of one or more at least equally unsaturated hydrocarbonimpurities, e. g. alpha-acetylenes and/or unconjugated diolefins, ispassed through a bed of the catalyst at a reaction temperature belowabout 375 C.; i. e. at a temperature below that at which conjugateddiolefins are rapidly decomposed upon contact with the cataLyst. Theminimum temperature at which the treatment may satisfactorily be carriedout varies somewhat depending upon the particular catalyst used. Forinstance, the decomposition of an alphaacetylene may be carried out at asatisfactorily rapid rate in the presence of cuprous oxide attemperatures as low as 140 C. and in the presence of any of the othercatalysts, e. g. copper, cupric oxide or iron or iron oxides, at about200 C'., or possibly at somewhat lower temperatures. As hereinbeforeindicated, the activity of the catalyst increases with increase in theratio of its,surface to its absolutevolume, e. g. as the particle sizethereof is decreased, and it may be possible to prepare the catalysts inphysical forms which will be effective at temperatures lower than thosejust mentioned. In practice, however, the treatment is usually carriedout at temperatures between 220 and 350 C., and preferably between 275and 325 C. The vapors are passed'over the catalyst at a rate sufficientto avoid destruction of more than a minor amount, e. g. less than 20,and preferably less than 10, per cent of the conjugated diolefin. Thetime of contact with the catalyst should, of course, be sufiicient tocause destruction of the major portion, and preferably all, of thehighly unsaturated hydrocarbon impurities initially accompanying theconjugated diolefin.

The heat required to initiate the reaction may be supplied by directheating of the catalyst bed or by preheating of the vapor mixture priorto flow into the bed. However, the reaction is highly exothermic and,once stated, further heating from an outside source may not benecessary. In some instances, cooling may be required in order tocontrol the reaction temperature.

The treatment is usually carried out at atmospheric pressure orthereabout, but it may be carried. out at lower or at much higherpressures, e. g. at pressures between 5 and pounds per square inch,absolute. By carrying the treatment out at a pressure above atmospheric,e. g. between 30 and 80.pounds per square inch, absolute, the conjugateddiolefln product may be readily cooled and liquefied without resortingto refrigeration or further compression of the same. The selectivereaction for the destruction of the highly unsaturated hydrocarbonimpurities occurs satisfactorily regardless of whether steam or otherinert gases are present in the vapors under treatment and, if desired,the reaction may be carried out under substantially adiabatic conditionsusing steam as a diluent for controlling the reaction temperature.Accordingly, the present method for the removal of such impuritiesthrough the bed.

jugated diolefin and such highly unsaturated hy-.

drocarbon impurity over they catalyst under the preferred conditionsdescribed above, the impurity may be entirely removed withoutappreciable loss of the conjugated diolefln or other hydrocarbons moresaturated than the diolefins initially present.

The following examples describe certain ways in which the principleof'the invention'hasbeen applied, but are not to be construed aslimiting the invention. 7

EXAMPLE .1

A chamber of 3 centimeters. internal diameter and 50 centimeters lengthwas filled with cupric oxide in wire form and the copper oxide wasreduced to metallic .copper with hydrogen. A

fraction of cracked-oil gas containing approximately 44.9 per cent byvolumeof butylenes (prin cipally butylene-l), 53 per cent ofbutadiene-1.3 and 1.9 per cent acetylenes (principally methylacetylene,ethyl-acetylene and vinyl-acetylene) was heated to about 270 C. and waspassed at a rate of 2.2 grams per minute into the bed of copper whilemaintaining the latter at the same temperature. The vapors passing fromthe bed were collected and analyzed. They were found to be entirely freeof acetylenes and to contain 48 per cent by volume of butadiene-1.3.

. Exmu 2 In each of a series of experiments, a chamber having thedimensions given in Example 1 was Table II Untreated gas Treated gasRate 6r.

Tcmp., No 7:3 "C Percent Per cent Percent mm w Blphib buta nippl butanewdicnc mtylenu dieno lam-S 2.2 2: 0 m 1.9 a: "0.9 2. 2.9 3.!" a; 1.9 540.0

EXAIIPL! 4 Exmts 3 In each of two experiments a fraction of cracked-oilgas containing the ingredients stated in Example 1 was passed through aheated chamber of 3' centimeters internal diameter and 50 centimeterslength, which chamber was filled with cupric oxide in wire form. Thegases issuing from the chamber were collected and an-. gives the percentby volume of alyzed. Table II butadiene-L3 and of alpha-acetylenes inthe gas mixture both before and after passage through the heatedchamber. It also gives the rate at which the gas mixture was fed intothe chamber and the average temperature within the chamber.

In each of a series of experiments, a crackedoil gas fraction containingthe ingredients stated Y in Example 1 was passed through a heatedchamber of .3 centimeters internal diameter and 50 centimeters length,which chamber was filled with r a powder of the catalytic substancenamed in the following table. The gases issuing from the chamber werecollected and analyzed. Table III names. the catalyst used in eachexperiment, gives the rate of flow of the hydrocarbon mixture, and

' states the average temperature within the catalyst bed. The tablestates the per cent by volume of butadiene-L3 and also of acetylenes inthe mixture,.both prior to and after passage over the catalyst.

Table III I I Untreated gas Treated gas Run No. Catalyst 2" Flow Percent Per cent Per cent Per cent butadiene acetylenes butadieneacetylenes 202 0.7 63 2.0 a l g 253 0.7 63 2.0 r 59 0 0 195 0.7 63 2.063 0 4 276 0.7 63 2.0 56 0 0 Exam 5 filled with powdered cuprous oxide,and a fraction of cracked-oil gas containing theingredients stated inExample 1 was heated and passed into the bed of cuprous oxide at a rateof -1.1

grams per minute. The gases issuing from the bed were collected andanalyzed. The following table gives the per cent by volume of butadiene-1.3 and also of alpha-acetylenes in the gaseous mixture which was fedinto the bed of cuprous oxide, the average temperature of the gaseswithin the bed, and the per cent of butadiene-L3 and of alpha-acetylenesin the gas after passage mately 21.3 per copper nitrate solutioncontaining approximately per cent'by weight oi'Cu(N0':) 2.3330,thereafter draining and drying the brick, and decom-' posing the coppernitrate toiorm copper oxide by heating the granular material to about500 C. in a current of air. An iron tube of 1 inch internal diameter wasfilled to a depth of 30" inches with the granular catalyst. 97.5 gramsof a cracked-oil gas fraction containing the ingredient's stated inExample 1 .and having an acetylene content or 1.9 per cent by volume waspassed through the tube at a rate of 2.5 grams per minute while heatingthe mixture within the catalyst chamber at a temperature ofapproximately300 C. After passage through the catalyst chamber, theremaininghydrocarbons were 1.6 grams of water.

analyzed for acetylenic hydrocarbons.

. equal parts by weight of butylene and butadienealso obtained in thecondensate Approximately 1.7 grams of carbon was formed during thetreatment.

1.3. There was EXAMPLE 6 A granular catalyst of from 4 to mesh particlesize and containing 25 per cent by weight of cupric oxide supported onSilocel brick was prepared as in Example 5. An iron chamber of 10 inchesinternal diameter and 20 inches depth was filled with the catalyst. Thecatalyst bed was brought-to a temperature of about 300 C. by passage ofa mixture of air and superheated steam therethrough, at which time theintroduction of air was discontinued, the chamber was swept free of airwith the steam, and the treatment of a diolefin-eontaining hydrocarbonvapor mixture to free the same of acetylenes was started. Thehydrocarbon mixture contained about 49 per cent by volume of butylenes,about 49 per cent of butadiene-1.3 and 2 per cent of acetylenes(principally methyl-acetylene, ethylacetylene and vinyl-acetylene). Theprocedure in carrying out the treatment was to pass the mixture(together in most instances with sufllcient steam to avoid thepossibility of local overheating within the catalyst bed due to the heatof reaction) over the catalyst at the pressure given in the followingtable while maintaining the mixture within the bed at temperaturesbetween 280 and 320 C. The vapors issuing from the bed were cooled,while under pressure, to condense the hydrocarbons and the latter werecontinuously The bya mixture of air and sufficient steam to preventexcessive temperature rises within the catalyst bed is passed throughthe latter until the bed is substantially free of carbon and the copperis re-oxidized to copper oxide. This operation is usually carried out attemperatures between 400 and 600 C., but higher temperatures, e. g.about 1000 C., have been used without damage to the catalyst. Forconvenience, the burning oil operation was carried out at about the samevapor pressure as that employed in freeing the hydrocarbon mixture ofacetylenes. After completing the burning ofi operation, passage of themixture of hydrocarbon vapors and steam over the catalyst wasresumed.These alternate operations of passing the hydrocarbon mixture over thecatalyst and of burning off the latter were repeated fourteen timeswithout appreciable decrease in the activity of the catalyst. The dataaccumulated is summarized in the following table which gives the poundsof the hydrocarbon vapors, and also of steam, fed into the catalyst bedper hour, the pressure at which the treatment was carried out, the totalweight of hydrocarbons fed into the bed in each cycle of the process,the length of time over which the hydrocarbon mixture was passed throughthe catalyst in each cycle and the time of heating in each "burn offoperation. It may be mentioned that during the operations for theremoval of acetylenes from the hydrocarbon mixture the proportion ofsteam was varied for purpose of tempera ture control and that there werebrief periods in which the introduction of steam was interrupted. In thetable, the step of treating the hydrocarbon mixture to remove acetylenesis referred to as operation A and the step of burning off the catalystis referred to as operadrocarbon products consisted almost entirely oftion B."

Table IV Rates of flow Abs. Lbs. 0! Duration of 15 &5: Hydny pressure,hydrocartreatment,

carbons Steam, lbs/in. bons treated hrs. lbsJhL' lbs./hr.

l A 7 60 21-23 28 4 B 21-23 1.25 2 A 7 60 21-23 42 6 1i 21-21 1.5 3 A7.6 16 21-23 19 25 B 21-% 1.5 4 A 7.3 0-20 21-23 44 6 B 21-23 1.75 5 A11.1 20-0 21-23 4.5 B i 21-23 2 6 A 9.2 12 21-23 6.5 B 21-23 1.3 7 A13.4 6-0 21-23 47 3.5 B 2l-Zi 3 8 A 13.4 5-20 35-55 57 4.25 B 35-55 3.59 A 26.3 0-30 35-55 97.5 3.7 B 35-55 4.5 10 A 28.6 30-50 35-55 71.5 2.5B 35-55 3.75 11 A 52 48 35-55 13 0.25 B 35-55 as 12 A 27.7 Unknown 35-5583 3 B 35-55 3 l3 A 47.5 Unknown 35-55 5 2 B 35-55 2. 75 14. A 60Unknown 35-55 l. 17

u ien -1. u t the time hen butylene and b tad e 3 p o w EXAMPLE 7 thecatalyst had become so badly fouled that acetylenes began to appear inthe products. Op-

eration in the manner ust described was interrupted before theproportion of acetylenes in the mixture issuing from the bed had risento a value of 0.05 per cent by volume, and the catalyst was freed ofcarbon and reactivated by a. "burning ofP'operation. In thisburning ofioperation,

chamber of 3 centimeters internal diameter and 50 centimeters length,which chamber was filled with cupric oxide in wire form. Anotherportion, of the mixture was passed through a heated chamber having thesame dimensions, but filled with ferric oxide powder. In eachexperimentthe rate of fiow was 0.3. liter of the gas mixture (measuredat 25 C. and atmospheric pressure) per minute. In each instance, the gasissuing from said chamber was collected and analyzed for allene. Thefollowing table names the catalyst used in each experiment, states theaverage temperature within the bed of catalyst and gives the per cent-byweight of alleue in the treated gas.

Table V Percent Run No. Catalyst Temp., "C. alleue in treated gas 1-.CuO. 300 2. 9 3 Fel a-n-n- 290 Exams: 8

' ature of the catalyst bed and the results obtained.

Table VI states the average temperature within the catalyst bed for eachexperiment and" gives class consisting of copper, iron, and the oxides.iugated diolefin in a form substantially free of the same.

2.- The method which comprises passing a va- .por mixture containing aconjugated diolefin as the principal hydrocarbon ingredient having adegree of unsaturation as great as that of a diolefln and alsocontaining a minor amount of an alpha-beta-unsaturated aliphatichydrocarbon having no hydrogen atoms attached to the beta-carbon atomthereof into contact with a finely divided substance selected from theclass consisting of copper and iron and the oxides of said metals at areaction temperature be1ow350 0., the rate of vaporfiow beingsufilcientto avoid destruction of more than 10 percent of the conthe percent by weight of alleue retained in the gas after passage throughthe'bed of catalyst. Table VI a Per cent Run No. Temp., C. alleue intreatedgas In the following claims where a substance is referred to asbeing "finely divided" it will be understood that it may be in the formof a pow- I der, or fine grindings, or turnings, or it maybe depositedin dispersed form on or within a solid carrier material, or it may be in,the form or lumps, granules or rods, etc., having a fine porousstructure. a

Other modes of applying the principle of the invention may beemployedinstead of those explained, change being made as regards the :methodherein disclosed, provided the step or steps stated by any of thefollowing claims or the equivalent of such stated step or steps beemployed. a

I therefore particularly point out and distinctly claim as myinventionz'l. The method which comprises passing a vapor mixture, containing aconjugated diolefin as the principal hydrocarbon ingredient having adegree of unsaturation as great as that 01 a diolefin and alsocontaining, as an impurity incident to the manufacture of the conjugateddiolefin, a minor amount of a difierent and at least equally unsaturatedhydrocarbon, into contact with a finely divided substance selected fromthe jugated diolefin during passage of the vapors through the bed ofsaid finely divided substance.

3. The method as described inclaim 2, wherein the unsaturatedhydrocarbon having no hydrogen atoms on a beta carbon atom thereof is a1.2-diolefin.

4. The method as described in claim 2, wherein the unsaturatedhydrocarbon having no hydrogen atoms on a beta carbon atom thereof is a1.2-diolefin and the finely divided substance is a copper oxide. 3 g

,5. The method'as described in claim 2, wherein the conjugated diolefinis butadiene l.3, the unsaturated hydrocarbon having no hydrogen atomson a beta carbon atom thereof is allene, and the mixture into contactwith a finely divided sub-- stance selected from the class consisting ofcopper, iron, and the oxides of said metals. at .a reaction temperaturebelow 375 C.

7. A method or treating a vapor mixture con taining a conjugateddiolefln as the principal hydrocarbon ingredient having a degree, ofunsaturation as great as that of a dioieiln and also containing a minoramountof at least one alpha-,-

acetylene to destroy and remove the latter which i comprises passing themixture through a bed of a finely divided substance selected from theclass consisting of copper and iron and the oxides of said metals at areaction temperature below 325,

0., the rate of vapor flow being sumcient to avoid destruction of morethan 10 per cent of the conjugated diolefin during passage of the vaporsthrough the bed. a a

8. A method of treating a hydrocarbon vapor mixture containing aconjugated 'diolenn as the principal hydrocarbon ingredient havinga'degree of unsaturation as greatas that of a diolefin and alsocontaining a smaller amount of at least one alpha-acetylene to destroyand remove the latter which comprises passing such vapor mixture througha catalyst bed comprising, as an active ingredient, a finely'dividedsubstance selected from the class consisting of copper, iron, and theoxides of said metals, at a reaction temperature below 325 C. and at arate of vapor 'fiow sumcient to avoid destruction oi morethan ing thecarbon with an oxygen-containing gas.

9. A method or treating a vapor mixture containing a conjugated diolefinas the principal hydrocarbon ingredient having a degree of unsaturationas great as that of a. diolefin and also containing a minor amount of analpha-acetylene to destroy and remove the latter which comprises passingthe mixture over an oxide of copper at a reaction temperature below 375C. and at a rate of flow sufllcient to avoid destruction of more than 10per cent of the conjugated diolefin.

10. A method of treating a vapor mixture containing a conjugateddiolefin as the principal hydrocarbon ingredient having a degree ofunsaturation as great as that of a diolefin and also containing a minoramount of an alpha-acetylene to destroy and remove the latter whichcomprises passing the mixture over cuprous oxide at a reactiontemperature between 140 and 350 C. and at a rate of flow suflicient toavoid destruction of more than 10 per cent of the conjugated diolefin.

11. A method of treating ajhydrocarbon vapor mixture containingbutadiene-1.3 as the principal hydrocarbon ingredient having a degree ofunsaturation as great as that of a diolefin and a minor amount of atleast one alpha-acetylene having from three to four carbon atoms in themolecule to destroy and remove the alpha-acetylene, which comprisespassing the mixture over an oxide of copper at a reaction temperaturebetween 275" and 325 C. and at a rate or flow sufiicient to avoiddestruction of more than 10 per cent of the butadiene.

ture and removing carbon from said bed by burn- 12. A method of treatinga vapor mixture containing a conjugated diolefin as the principalhydrocarbon ingredient having a degree of unsaturation as great as thatof a diolefin and also containing a minor amount of an alpha-acetyleneto destroy and remove the latter which comprises passing the mixtureover an oxide of iron at a reaction temperature below 375 C. and at arate of flow sufficient to avoid destruction of more than 10 per cent ofthe conjugated diolefin.

13. A method of treating a hydrocarbon vapor mixture containing aconjugated diolefin as the principal hydrocarbon ingredient having adegree of unsaturation as great as that of a diolefin and alsocontaining a minor amount of at least one alpha-acetylene to destroy andremove the latter which comprises passing the mixture over an oxide ofiron at a reaction temperature between 225 and 350 C. and at a rate offlow suflicient to avoid destruction of more than 10 per cent of theconjugated diolefin.

' 14. A method of treating a hydrocarbon vapor mixture containingbutadiene as the principal hydrocarbon ingredient having a degree ofunsaturation as great as that of a diolefin and a minor amount of atleast one alpha-acetylene having from 3 to 4 carbon atoms in themolecule to destroy and remove the alpha-acetylene, which comprisespassing the mixture over an oxide of iron at a reaction temperaturebetween 275 and 325 C. and at a rate of flow sufficient to avoiddestruction of more than 10 per cent of the butadiene.

LUDO K. FREVEL.

